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Biomedical subjects

R Shapiro

Publications and source records attributed to R Shapiro.

At least 343 records · Page 19Linked to original sources
PubMed1987

Observation of a chloride-dependent intermediate during catalysis by angiotensin converting enzyme using radiationless energy transfer.

Stopped-flow radiationless energy-transfer kinetics have been used to examine the effects of chloride on the hydrolysis of Dns-Lys-Phe-Ala-Arg by angiotensin converting enzyme. The kinetic constants for hydrolysis at pH 7.5 and 22 degrees C in the presence of 300 mM sodium chloride were KM = 28 microM and kcat = 110 s-1, and in its absence, KM = 240 microM and kcat = 68 s-1. The apparent binding constant for chloride was 4 mM, and the extent of chloride activation in terms of kcat/KM was 14-fold. The effects of chloride on the pre-steady-state were examined at 2 degrees C. In the presence of chloride, two distinct enzyme-substrate complexes were observed, suggesting multiple steps in substrate binding. The initial complex was formed during the mixing period (kobsd greater than 200 s-1) while the second complex was formed much more slowly (kobsd = 40 s-1 when [S] = 5 microM and [NaCl] = 150 mM). Strikingly, in the absence of chloride, only a single, rapidly formed enzyme-substrate complex was observed. These results are consistent with a nonessential activator kinetic mechanism in which the slow step reflects conversion of an initially formed complex, (E X Cl- X S)1, to a more tightly bound complex, (E X Cl- X S)2.

Animals↗
PubMed1987

Dermatologic findings associated with human immunodeficiency virus infection.

Both human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) are associated with an increased prevalence of several dermatologic diseases. We studied healthy homosexual men with negative reactivity to HIV antibody, homosexual men without AIDS but with positive reactivity to HIV antibody, and homosexual men with AIDS to compare the prevalence of dermatologic disease in these groups. We found that five cutaneous disorders were increased in persons with HIV infection. Oral hairy leukoplakia was increased both in seropositive subjects without AIDS and in subjects with AIDS. Condylomata acuminata and seborrheic dermatitis were slightly increased in seropositive non-AIDS subjects and significantly increased in the AIDS group. Molluscum contagiosum and oral candidiasis were increased only in the AIDS group.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Ribonucleolytic activity of angiogenin: essential histidine, lysine, and arginine residues.

The homology of angiogenin and pancreatic RNase A provides a compelling reason to systematically compare the characteristics of the two proteins using the chemical modification approaches that proved essential to understanding the action of RNase. Reagents specific for histidine, lysine, and arginine markedly decrease the ribonucleolytic activity of angiogenin, much as has been observed for RNase A. Activity is abolished by reduction of the disulfide bonds and is restored by reoxidation. Methionine, tyrosine, and carboxyl group reagents have no significant effect. From the point of view of reactivity, the histidine and lysine residues in angiogenin are severalfold less susceptible to modification than those in RNase A. Arginine reagents, on the other hand, inactivate angiogenin considerably faster than RNase A. Considering specificity, bromoacetate inactivates angiogenin at pH 5.5 by modifying 1.5 histidines, but lysine and arginine reagents are less specific. Thus, 3.8 and 6.3 residues, respectively, are modified by 1-fluoro-2,4-dinitrobenzene and by formaldehyde plus cyanoborohydride, under conditions where activity decreases by approximately 80% in both cases. With phenylglyoxal, 6.7 arginines are lost when there is 92% inactivation. Poly(G) prevents inactivation by lysine and arginine reagents, and phosphate protects against the effects of lysine modification. Thus, the functional consequences of these modifications likely reflect the loss of critical residues rather than general conformational effects.

Arginine↗
PubMed1987

Human placental ribonuclease inhibitor abolishes both angiogenic and ribonucleolytic activities of angiogenin.

Human placental ribonuclease inhibitor (PRI) abolishes both the ribonucleolytic activity of angiogenin toward 28S and 18S rRNA and its angiogenic activity on the chicken embryo chorioallantoic membrane. Treatment of the angiogenin-PRI complex with p-hydroxymercuribenzoate releases enzymatically active angiogenin. Assays measuring competition between angiogenin and bovine pancreatic ribonuclease A for PRI reveal that binding of the inhibitor to angiogenin is extremely tight, with a Ki value well below 0.1 nM. The stability of the angiogenin-PRI complex was assessed by cation-exchange HPLC quantitation of free angiogenin. No significant dissociation was detected after 17 hr at 25 degrees C in the presence of a large excess of bovine ribonuclease, which serves as a scavenger for free inhibitor. The results of these experiments, based on the predictive capacity of the angiogenin/RNase homology, suggest that PRI and related inhibitors may participate in the in vivo regulation of angiogenin and that this might have pharmacologic and/or therapeutic implications.

Allantois↗
PubMed1987

Urinary thromboxane excretion in cardiac allograft rejection in immunosuppressed rats.

Increased urinary excretion of immunoreactive thromboxane B2 (iTxB2) was found to have a high predictive value, with high sensitivity as an indicator of cardiac allograft rejection in both the immunosuppressed and nonimmunosuppressed rat. In the animals receiving an allograft, urinary iTxB2 excretion significantly increased prior to the onset of rejection, remained elevated, and returned to basal values following completion of the episode. Urinary iTxB2 remained at baseline values in the control animals. The association between rejection and iTxB2 excretion was preserved regardless of the presence or nature of immunosuppression. Urinary iTxB2 excretion increased significantly prior to the reduction of graft beat or histological evidence of rejection. Evaluation of urinary iTxB2 monitoring as a noninvasive indicator for surveillance of clinical cardiac allograft rejection appears to be warranted.

Animals↗
PubMed1986

Isolation and characterization of a human colon carcinoma-secreted enzyme with pancreatic ribonuclease-like activity.

A ribonuclease was isolated from serum-free supernatants of the human colon adenocarcinoma cell line HT-29. It was purified by cation-exchange and C18 reversed-phase high-performance liquid chromatography. The protein is basic, has a molecular weight of approximately 16,000, and has an amino acid composition that is significantly different from that of human pancreatic ribonuclease. The amino terminus is blocked, and the carboxyl-terminal residue is glycine. The catalytic properties of this ribonuclease resemble those of the pancreatic ribonucleases in numerous respects. Thus, it exhibits a pH optimum of approximately 6 for dinucleotide cleavage and employs a two-step mechanism in which transphosphorylation to a cyclic 2',3'-phosphate is followed by slower hydrolysis to produce a 3'-phosphate. It does not cleave NpN' substrates in which adenosine or guanosine is at the N position and prefers purines at the N' position. Like bovine ribonuclease A, the HT-29-derived ribonuclease is inactivated by reductive methylation or by treatment with iodoacetate at pH 5.5 and is strongly inhibited by the human placental ribonuclease inhibitor. However, in contrast, the tumor enzyme does not cleave CpN bonds at an appreciable rate and prefers poly(uridylic acid) as substrate 1000-fold over poly(cytidylic acid). It also hydrolyzes cytidine cyclic 2',3'-phosphate at least 100 times more slowly than uridine cyclic 2',3'-phosphate and is inhibited much less strongly by cytidine 2'-monophosphate than by uridine 2'-monophosphate. Other ribonucleases known to prefer poly(uridylic acid) were isolated both from human serum and from liver and were compared with the tumor enzyme. The physical, functional, and chromatographic properties of the serum ribonuclease are essentially identical with those of the tumor enzyme. The liver enzymes, however, differ markedly from the HT-29 ribonuclease. The potential utility of the tumor ribonuclease in the diagnosis of cancer is considered.

Adenocarcinoma↗
PubMed1986

Characteristic ribonucleolytic activity of human angiogenin.

Angiogenin, a blood vessel inducing protein isolated from a human tumor cell line, has been found to exhibit ribonucleolytic activity. It catalyzes the cleavage of both 28S and 18S ribosomal RNA as determined by agarose gel electrophoresis. The major products formed with these substrates are 100-500 nucleotides in length. In contrast, angiogenin is inactive toward all of the more conventional substrates of the homologous pancreatic ribonucleases. In particular, it does not produce detectable amounts of acid-soluble fragments from high molecular weight wheat germ RNA, poly(C), or poly(U), nor does it hydrolyze cytidine or uridine cyclic 2',3'-phosphate. The high degree of sequence homology between angiogenin and the pancreatic ribonucleases, which includes all three catalytic residues, His-12, Lys-41, and His-119, has thus identified the chemical nature of a potential angiogenin substrate. These results may bear importantly on the physiological function of angiogenin.

Adenocarcinoma↗
PubMed1986

Conformation of d(CpG) modified by the carcinogen 4-aminobiphenyl: a combined experimental and theoretical analysis.

The change in DNA conformation produced by the attachment of a reactive substance is likely to be a vital factor in determining the biological consequences of the reaction. We have prepared a deoxydinucleoside monophosphate containing the major adduct derived from the carcinogenic amine 4-aminobiphenyl and analyzed its conformation by theoretical and experimental methods. Reaction of d(CpG) with N-acetoxy-N-(trifluoroacetyl)-4-aminobiphenyl afforded the product modified at C-8 of guanine with 4-aminobiphenyl. After purification by reverse-phase high-performance liquid chromatography, milligram amounts of product were obtained. It was analyzed by circular dichroism, proton magnetic resonance, and minimized potential-energy calculations. A flexible molecule with a mixture of conformers is indicated. Both carcinogen-base-stacked states and base-base-stacked states, with guanine both syn anti, contribute to the population mixture on the dimer level. The global minimum-energy conformation has syn-guanine and carcinogen-base stacking. Forms of this type are calculated to represent roughly 58% of the conformer population. Because of the twisted nature of the biphenyl moiety, carcinogen-base stacking inherently involves less overlap than that in the planar and rigid three-ringed aminofluorene analogue. This difference might relate to the diminished effectiveness of the aminobiphenyl vs. the aminofluorene adduct as a frameshift mutagen in Salmonella typhimurium 1538.

Aminobiphenyl Compounds↗
PubMed1986

Gas vitrectomy in a primate model.

Total displacement of vitreous by an expanding bubble of a perfluorocarbon gas was studied in cynomolgus monkeys. The clinical observations and the gross dissection suggested that cortical vitreous might have been stripped from the retina; however, electron microscopy of frozen sections demonstrated that the collagen structure of the vitreous was compressed against the retina.

Animals↗
PubMed1986

Minimal asymmetry of the brain: a normal variant.

Normal cerebral asymmetry, well-known to neuroradiologists, is not widely recognized by radiologists in general. In our review of CT brain scans, 31 of 300 patients with a negative neurologic examination and no history of birth injury, head trauma, or seizure had recognizable asymmetry of the frontal horns of the lateral ventricles. The right frontal horn and the right cerebral hemispheres were larger than the left twice as often as left were larger than right. The right frontal lobe was wider than the left in 44% of patients and extended as far anteriorly or more anteriorly than the left in 22% of patients. The right central hemispheric mass tended to be wider than the left, resulting in slight displacement of the pineal gland to the left, in approximately 45% of cases. The posterior end of the left Sylvian fissure projected farther posteriorly in 10% of the patients. Occipital petalia and a more posterior position of the calcified glomus of the choroid plexus of the lateral ventricle were both common on the left side of 56%. Earlier studies of the brain by other methods have also shown asymmetry. An awareness of these anatomic asymmetries in normal individuals should preclude the erroneous diagnosis of an atropic or mass lesion.

Adolescent↗
PubMed1986

Complement activation by 19S IgM rheumatoid factor: relationship to disease activity in rheumatoid arthritis.

19S IgM rheumatoid factor (RF) in rheumatoid arthritis (RA) are polyclonal autoantibodies directed against the Fc piece of IgG. Rheumatoid patients with RF tend to have aggressive synovitis, nodules, and extraarticular manifestations. Although RF titer does not correlate with disease activity, RF activates complement (C) by the classical pathway. Thus, we postulated that selective stimulation of cell clones producing efficient C activating RF molecules might be associated with disease flares, independent of changes in serum RF concentration. To address the question, 42 patients with RA were evaluated prospectively. Serum RF concentration was measured by radioimmunoassay (RIA) and C activating activity by hemolytic assay. We then calculated the mean hemolysis (MH) of sensitized sheep erythrocytes (SRC) produced/ml of RF serum (MH/ml) and MH/microgram of RF as an expression of RF C activating properties (CAP). The following observations were made: RF CAP varied among the patients studied; RF CAP varied over time in individual patients; RF CAP differences varied in both groups independently from RF concentration; RF CAP correlated with both systemic and articular disease activity; and total RF concentration correlated with articular findings and nodules but less well with systemic disease activity.

Adult↗
PubMed1986

Reactions of nucleosides with glyoxal and acrolein.

The structural determination of the products formed by the reaction of derivatives of glyoxal with guanine are reviewed, as are the applications of these reactions. Conditions have now been defined for the use of glyoxal as a probe for microdetermination of the structure of unidentified nucleic acid components. Unexpectedly, 3-methylguanine shows a positive reaction with glyoxal. The adduct produced has been isolated and characterized. A new ring is formed by substitution at the 1- and N2-positions of 3-methylguanine in this product. Acrolein reacts smoothly with 1-methylcytosine, cytidine and deoxycytidine at pH 4. The structures of the adducts have been determined. The amino group of cytosine adds to the double bond of acrolein, while the aldehyde binds to the 3-position, forming a new ring. Adenosine, deoxyadenosine and 9-methyladenine react in an analogous manner with acrolein, with ring formation involving the amino group and the N-1 of adenine. The orientation of addition is similar to that in the cytosine series. Guanosine reacts with excess acrolein at pH 4 to form a bis-adduct. Two new rings are fused to the guanine structure, one at N-1 and the amino group, and the other involving N-7 and C-8. A number of derivatives of this product have been obtained by glycosyl cleavage and imidazole-ring-opening reactions. However, the assignment of the orientation of addition for both acroleins remains tentative in this series.

Acrolein↗
PubMed1986

Management of the undescended thyroid.

Ectopic thyroid can occur throughout the neck but is found most commonly at the tongue base. Management includes Tc99m radionuclide scanning to confirm the presence and location of the thyroid tissue. Dysfunction should be assessed by T4, TSH, and thyroid antibody testing. Hormonal therapy is the primary treatment but surgery may be necessary in cases of airway obstruction. Six children with undescended thyroid are presented and a management protocol based on the presence or lack of symptomatology is proposed.

Child↗